1. Field of the Invention
The present invention relates to a heating apparatus utilizing induction heating, and more particularly to a fixing apparatus which fixes a toner which can be utilized in an electrophotographic type copying apparatus or a printer apparatus using a toner having the thermofusion property as a visualization agent.
2. Description of the Related Art
A fixing apparatus incorporated in a copying apparatus using an electrophotographic process heats and melts a toner formed on a transfer medium, and fixes the toner on the transfer medium.
As a method of heating the toner which can be utilized in the fixing apparatus, a method of using the heat radiated from a filament lamp, a flash fixing method using a flash lamp, or the like is well known. It is to be noted that a fixing apparatus using an induction heating device which utilizes heat generation of a metal caused due to electromagnetic induction has also come into practical use in recent years.
Further, in many cases, there are used a heat (fixing) roller having a heater set therein and a pressure roller which is pressed against the heat roller at one point on the outer periphery of the heat roller by a predetermined pressure. According to this structure, it is well known that the heat of the heat roller can be efficiently supplied to the toner and also that a pressure used to fix the melted toner to the transfer medium can be readily supplied to the transfer medium and the toner.
Nowadays, the induction heating type heating apparatus is extensively utilized since its time required for increasing a temperature of the surface of the heat roller is shorter than that of a heating apparatus which is of a type using a filament lamp as a heat source.
Meanwhile, in many fixing apparatuses each using the induction heating type heating apparatus, a general-purpose circuit called, e.g., the semi E class is utilized for the purpose of lowering a cost of a drive circuit which supplies a predetermined power to an induction coil which generates an eddy current in the heat roller in order to increase a temperature of the heat roller.
In case of using the semi E class general-purpose circuit, however, a current of several-ten ampere flows through the induction coil due to an impedance of an inverter circuit including the induction coil. This has a problem of an increase in a cross section of an electric wire used in the induction coil.
On the other hand, as the electric wire used in the induction coil, e.g., an expensive litz wire must be used in order to avoid the influence of the skin effect which becomes prominent when a frequency of the current inputted to the coil is changed to a high frequency.
Furthermore, since a size of the induction coil is increased owing to a fact that an electric wire with a large cross section must be used, an outside diameter of the heat roller is disadvantageously increased when the induction coil is arranged inside the heat roller in order to increase the utilization efficiency of a magnetic flux generated from the induction coil.
It is to be noted that there may occur a problem of generation of the flicker that a light quantity of the light radiated from an illumination equipment arranged in a surrounding area, especially a discharge lamp such as a fluorescent lamp due to an intensity of the current flowing through the inverter circuit, i.e., the induction coil when the current is supplied to the induction coil from a non-energization state or when the current supplied to the induction coil is interrupted.